Posts Tagged flood

From a natural disaster perspective, Australia is having a much worse year than New Zealand, despite our apparent penchant for earthquakes, volcanic eruptions, flooding, and the occasional crippling winter storm on this side of the ditch. To date, the Insurance Council of Australia has officially declared three natural disasters in 2013 (the Tasmanian bush fires, New South Wales bush fires, and cyclone Oswald). But is Australia’s exceptional season for extreme weather just a blip on an otherwise “normal” climate regime, or is it perhaps a harbinger of worse things to come as our climate continues to warm?

Worse than the Queensland flooding of 2011?

Our poor neighbours across the ditch have been enduring scorching temperatures and raging bush fires for nearly a month, and now the east of the country is being thrashed by extreme weather, this time of the wet variety, courtesy of cyclone Oswald. Just over a year after Australian Prime Minister Julia Gillard called the Queensland floods (December 2011 version) “the worst natural disaster in our history” , Queensland and northeastern NSW are once again being battered by extremely stormy weather, including widespread flooding and tornadoes.

Four people have been already been killed by flooding and storm-related hazards in Queensland, since cyclone Oswald made landfall. Communities such as Bundaberg in Queensland and Grafton in New South Wales are experiencing the worst flooding on record, while parts of Sydney have seen the heaviest rainfalls in over a decade.

The link between extreme weather and climate change

So do these recent extreme-weather-related natural disasters indicate that Australia’s climate is becoming more extreme in a broader sense? After all, heat waves and bush fires have historically been a regular fixture of the Australian climate; the same can be said for tropical storms which affect the east coast of Australia.

Actually, these types of extreme weather have become more frequent, and more severe in recent decades. A few decades ago in Australia, the number of new record high temperatures each year was approximately balanced by the number of new record low temperatures. Recently, the ratio of new record highs to new record lows has increased to 2:1. In 2010, 19 countries set new all-time record highs, but no new low temperature records were set.

Climate warming doesn’t directly cause natural disasters like heat waves, bush fires and tropical storms, but it can contribute to more extreme weather in several ways, including:

A warmer atmosphere can hold more water vapour, increasing the risk of extreme precipitation,

Higher temperatures increase the rate of evaporation from soil and water surfaces, as well as evapotranspiration by plants, increasing the frequency and intensity of droughts,

Higher sea-surface temperatures can cause changes in oceanic and atmospheric circulation patterns, which are driven by gradients in temperature and salinity,

Warming oceans provide more energy for the development of tropical storms,

Rising sea level due to melting ice means that many populated areas are increasingly at risk from tsunami and storm surges.

Weather now develops in different climatic conditions than it did just a few decades ago; heat waves are longer and hotter, tropical storms are more frequent and more intense, as are periods of drought. The cold(?) hard reality is that extreme weather events that can contribute to natural disasters are on the increase.

The graph below illustrates why a small increase in mean annual temperature can shift the climate curve so that extreme heat events become more severe, and much more frequent. Case in point; the extremely hot conditions of this Australian summer are difficult to attribute to a simple blip on an otherwise normal climate regime; far from just a few days of unusually hot weather, much of Australia has been baking for months. A new record was set for average maximum daytime temperatures during the last 4 months of 2012 (which were 1.6 degrees above average ).

Solomon et al. 2007

The hottest day ever in Australia: blistering heat and bush fires

Since the new year, fire-fighting crews have battled hundreds of bush fires in south-east Australia, including in New South Wales, Victoria and Tasmania. Prolonged extreme heat combined with high winds to create ideal fire conditions. Average maximum temperatures across the country soared to 40.33 degrees on 7 January, the hottest day ever recorded over the Australian continent; even the Tasmanian capital Hobart reaching nearly 41 degrees. For the first time ever, the continent recorded five consecutive days with an average temperature exceeding 39 degrees; each of the first six days of 2013 were amongst the 20 hottest days on record.

1.6 degrees above average is a startling increase when averaged over a four month period, but it isn’t just Australia that has been experiencing a warmer climate: according to the Climate Change Research Centre (University of NSW), the number of very warm days (defined by the warmest 5% of days between 1950 and 1980) has increased by nearly 40% globally since 1983.

Whatever the sceptics may say, our climate is becoming more extreme, and Australia is merely the latest place to suffer from the effects of global warming.

Rain-laden clouds from the north Tasman sea settled over the top of the south island several days ago, and have been drenching the Nelson and Golden Bay regions ever since. Extreme rainfall has been recorded in Takaka, Richmond and Nelson, with the Kotinga gauge at Takaka recordind an unprecedented 423mm in 24 hours. The estimated 24 hour rainfall for a 1-in-100 year event at Takaka is 380mm (Tasman district council here). The previous highest recorded 24-hour rainfall from the Kotinga gauge was 216.5mm in 1995.

Saturated hillsides have given way in many locations, with landslides and debris torrents reportedly causing widespread damage in the region (stuff.co.nz story here).

Flooding, Nelson. Photo: Tim Bow

Landslide, Nelson. Source: The Nelson Mail

Flooding, Nelson. source: stuff.co.nz

Backyard Swimming Hole. Source: stuff.co.nz

Fortunately, all the news is not bad, as the rain has been easing, with heavy precipitation moving towards the North Island, where Taranaki, Northland and the Bay of Plenty can expect up to 150mm of rain.

Global Economic Hub
Thailand is a global manufacturing hub, and a leading exporter of automobiles, electronics, textiles, clothing and food. Exports of goods and services accounting for approximately 70% of Thailands’ GDP in 2010. Tourism has largely recovered following the Indian Ocean tsunami (which claimed more the 5000 lives in Thailand), accounting for about 6% of GDP in 2010.

Many of the world’s largest auto manufacturers have major factories in Thailand, including Toyota, Honda, Nissan and Ford. As the world’s largest manufacturer and exporter of hard-disk drives, Thailand hosts hard-disk giants Western Digital, and Seagate Technology. Sony, Toshiba, Apple and Canon also rely on their Thailand manufacturing facilities to supply the global demand for consumer electronics.

Worst Flooding in 50 years

Since flooding began in northern Thailand in July of this year, the country has been coping with another deadly natural disaster; one that will also have global economic implications. With a mean rainfall of nearly 800 mm for the three-month period from August to October, Bangkok is no stranger to flooding, but an exceptionally wet monsoon season in the north has brought the worst flooding in over 50 years. Swollen rivers and floodwaters have gradually made their way towards the south, threatening the most populated regions surrounding the bay of Bangkok. Thailand is a country of 67 million people, with an estimated 9 million living in the capital city of Bangkok, where much of the city is merely 2 metres above mean sea level. The immediate impacts of the disaster have only begun to materialize:

â€¢ nearly 400 lives lost to date

â€¢ more than 100,000 people displaced from homes

â€¢ one-third of the country inundated, including major agricultural and industrial areas

â€¢ damage estimates >$6 billion US dollars

As Bangkok braces for another day, 1.2 billion cubic metres of flood water is expected to peak around the same time as high tide. Government officials have thrown in the towel in the fight to contain the rising flood waters. As low-lying areas of the city become inundated, thousands of people continue to flee the capital for higher ground. Tourism officials issued travel warnings earlier today advising tourists that “flooding in Bangkok now appears imminent”. Indeed.

Submerged Cars at Honda Factory in Thailand

Global Economic Implications
It may be the long-term economic impacts of this disaster that are most damaging. Consumers around the world will soon face the consequences of the temporary crippling of Thailand as a global manufacturing hub. Only time will tell what the extent of physical damage will be in Bangkok, but the economic impacts are already beginning to mount. The Thai government has imposed a 5 day “weekend” to allow people to cope with the disaster, and production at many major companies has already been stalled for much longer than that. Toyota has had to keep its’ Thai production suspended for nearly 4 weeks so far, reducing its’ ability to supply the Asian, North American and South African markets. In turn, the loss of parts produced in Thailand has forced Toyota to slow down its’ operations in other countries, including Japan, the Unites States, and Indonesia.

Toyota is not alone. Many other manufacturing companies spanning a wide range of industries have been impacted by the flooding. The economic impacts of this disaster will soon be brought home to us all, in the form of decreased availability, and higher prices on many goods, including automobiles, electronics, clothing, and food.

As has been the case with many recent flood disasters (eg. Pakistan in 2010), this years flooding in Thailand may have been exacerbated by human activity (or inactivity in this case). Despite high precipitation in northern Thailand at the beginning of the monsoon season, some down-steam water storage reservoirs were not drawn down enough in the early stages of flooding, leaving less capacity for temporary storage of flood waters. But that is a topic for another post.

Can We Blame Climate Change for Flooding in Venezuela & Columbia?

In recent weeks, the wettest rainy season in over 40 years has battered Columbia and Venezuela, with flooding and landslides claiming over 200 lives, forcing millions of people from their homes and inundating valuable agricultural crops. Over 1.6 million (nearly 4% of Columbia’s total population of 45 million) people have been displaced from their homes, primarily by flooding.

Venezuelan president Hugo Chavez has publicly blamed global climate change for the recent wet weather, pointing the finger at western-based “criminal capitalism” and overconsumption as the source of this latest natural disaster. Columbian president Juan Manuel Santos has described the events of recent weeks as an unprecedented tragedy for his country.

High rainfall isn’t unusual in the region. The mountainous topography of northern South America provides a barrier to trade winds from both the Pacific and Atlantic Oceans, forcing up warm, moisture-laden equatorial air currents. This generates potentially high rainfall in both the Pacific and Amazon regions, on either side of the continental divide. The town of Lloro in north western Columbia claims the highest average annual precipitation of any lowland location in the world, at 13.3 m.

Source: gaurdian.co.uk

This rainy season in Columbia has seen the heaviest rains on record. The result has been called the worst natural disaster in Columbia’s history. And like the flooding in Pakistan earlier this year, it is the high degree of vulnerability of the people who live in Columbia and Venezuela that has resulted in the massive scale of this disaster.

The 1999 Disaster in Venezuela

Caraballeda Venezuela, 1999. Source: USGS

Chavez should be familiar with the vulnerability of Venezuela’s growing population to natural disasters. In December 1999 (early in Chavez’s tenure), heavy rainfall events with an estimated return period of 1 in 20 to 1 in 50 years saturated the rugged northern coast of Venezuela, inducing many landslides along the Cordillera de la Costa. Many of these landslides swept down steep slopes and coalesced into debris flows which rushed down the narrow valleys and spread out across the alluvial fans where most people live. These debris flows swept through towns and cities with little advanced warning, destroying over 8000 buildings and resulting in the deaths of up to 30,000 people. In the worst-hit area Caraballeda, up to 6 m of bouldery debris inundated much of the city.

Caraballeda is no stranger to debris flows, like many other towns and cities along the rugged northern coastline of South America. Often the only flat areas large enough to support the growing towns and cities in the region are alluvial fans at the base of steep gullies or river valleys, which naturally concentrate flood waters and debris during major storms. In fact, these fans generally exist because they have been created by thousands of years of episodic flooding and debris flow activity. In Caraballeda, which had a history of several damaging debris flows before 1999, a channel engineered to convey debris flows through the city safely was inadequate, and quickly became inundated.

Following the tragedy of 1999, a report by the United States Geological Survey (USGS) made the following suggestions for mitigating future risk:

Of course, all of these things are economically costly, and require major government commitment. The gears of change turn slowly against political and economic resistance. In recent weeks, unstable saturated hillsides have mobilized again in Columbia and Venezuela, with landslides killing several hundred people in the region. Increased urbanization and agricultural intensification of river floodplains has left millions of people vulnerable to flooding.

Follow the link below to view a short video of a landslide in Columbia, September 2010:

Vulnerability to Natural Hazards

We must resist the temptation to blame the heavy precipitation in Columbia and Venezuela, and subsequent disaster, on a changing climate. Rather, we should recognize that this disaster is the result of people living on land that is normally subject to natural hazards like flooding and landsliding. Instead of immediately pointing the finger at climate change, we should be asking; why are people still living in areas prone to flooding and landslides, despite prior experience and warnings to the contrary? What can be done to make these places safer in the future?

Unfortunately, there is no easy way to reduce the vulnerability of people in such regions. Many of the people caught by this disaster haven’t been able to choose where they live. Housing shortages, innafordability and growing urban populations mean that many people are forced to live in dangerous areas, such as in valley bottoms subject to innundation, or on unstable hillsides. However, fundamental changes to land-use planning and a committment to educating the public about natural hazards may help to prevent such natural disasters in the future. If those issues aren’t addressed, regardless of whether or not climate change is driving more extreme precipitation events in Columbia and Venezuela, the region can expect a continued increase in the number and severity of natural disasters, as populations, and vulnerabilities increase.

“Amid Drought, Pakistan Prays for Rain”. That was the title of a National Geographic Daily News story published on 1 July, 2010. Since then, Pakistan’s scorching drought has indeed been remedied. Heavy monsoon rains over the past month have instigated widespread flooding, leading to the worst natural disaster in Pakistan’s history. As flood waters finally show signs of receding, the exceptional toll of the disaster is becoming clear:

over 17 million people displaced (approximately 10% of Pakistan’s population)

1600 lives lost

4.6 million people left homeless

Up to one fifth of the country inundated

Initial relief efforts will cost ~$460m US dollars

Recovery costs will be in the billions (US dollars)

Devastation of millions of hectares of fertile crop land and grazing land will have long term effects on Pakistan’s ability to produce food when they need it most

The food shortage in Pakistan will also have a global impact, as Pakistan is one of the world’s largest agricultural exporters

Source: Unitar/Unosat (click on image to enlarge)

The people of Pakistan have been having a rough go of it in recent years. Parts of northern Pakistan and Kashmir are still rebuilding following the 2005 Kashmir earthquake which resulted in over 80,000 deaths, and left 3.5 million people homeless. Many of these deaths occurred after the initial earthquake, as aftershocks, heavy rain, steep mountainous terrain and landslides ensured that critical transport links were blocked, slowing relief efforts. As is all too often the case with vulnerable populations, a lack of clean water, food, emergency shelter and medical supplies eventually took the greatest toll.

Earthquakes and flooding are simple facts of life in northern and western Pakistan, where the greatest mountain range in the world, the Himalaya, are actively being thrust up by the collision between the Indian subcontinent and the Eurasian plate. More than 50 million years of uplift has created the great topographic barrier of the Himalaya, which dramatically affects the climate of the region. Dry, cold Arctic winds are prevented from crossing the Himalaya into South Asia, keeping the Indian subcontinent relatively warm. During the northern hemisphere summer, moisture laden winds from the Indian ocean are gradually drawn northwards over the warm plains of southern India. Eventually these warm moist air currents collide with the Himalaya and cool as they are forced upwards, generating the summer monsoon rains that nourish the agricultural regions of India, Bangladesh, Nepal and Pakistan. The summer monsoon season in South Asia lasts for only a few weeks, but can generate some of the highest precipitation rates on earth. Some areas near the southern boundary of the Himalaya receive over 10 m of annual rainfall, the vast majority of which falls during the summer monsoon.

The Great Rivers

Several of the world’s great rivers, including the Ganges, Indus, Brahmaputra, Yangtze and Mekong originate in the Himalaya region. Approximately half of the world’s population (3 billion people) live within river drainages that are nourished by snowmelt and monsoon rains in the Himalaya.

A Hazardous Place

Scientists know that flooding, drought, earthquakes, and landslides have been occurring in South Asia for millions of years. There is nothing about these events that should catch us by surprise. The evidence of past events is recorded in the very landscape itself. Before our eyes is the greatest mountain range on earth, still being rapidly uplifted by astounding tectonic forces where two continental plates collide. Some of the world’s greatest rivers systems cut entirely through the immense topographic barrier of the Himalaya, in areas subject to some of the highest seasonal rainfalls on earth. Great gorges and rugged mountains give way to the largest river deltas in the world, reminding us that phenomenal volumes of sediment are being actively moved from the mountain highlands to nourish great floodplains, where half the world’s population lives, and makes a living off of the fertile land.

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